The present invention relates to improvements in a floppy disk unit which is to be used as an external storage device such as a personal computer and a word processor.
Electronic equipments such as a personal computer having been made more highly efficient and smaller increasingly in recent years. With this tendency, it is demanded that floppy disk units are made further smaller in size and produced at a lower cost. Concerning the dimensions of a floppy disk unit, there is a limit in miniaturization of the shape in plan on account of the standardized dimensions of a recording medium that is called a floppy disk or diskette. On the other hand, height of the unit greatly depends on a magnetic head, a driving mechanism, a floppy disk loading/unloading mechanism and a rotary driving device so that these components are considered as the object of improvement for realizing the miniaturization.
The rotary driving device of the floppy disk unit generally adopts an oilless metal of powdered sintered alloy as a bearing member. The oilless metal is press-fitted in a holder or housing of a bearing portion and, thereafter, subjected to sizing work to meet required dimensions. The oilless metal is suitable to make the floppy disk rotate in stable manner, and however, in order to provide a holding force large enough to tolerate the sizing work by press-fitting, a certain length is needed, with the result that the bearing portion is prevented from being made smaller in size. Examples of the sizing work for electric motors are seen in, for instance, Japanese Utility Model Unexamined Publication Nos. 62-54584, 64-23767 and 64-35532.
Further, in order to keep compatibility, it is necessary for the floppy disk unit to adjust the position of magnetic heads with respect to the floppy disk at the manufacturing stage. The floppy disk unit is provided with an adjustment portion for this purpose. Heretofore, for the rotating position of the floppy disk, an alignment medium has been used in which the angle is represented by time and a reference signal for adjustment called "index burst" or "time burst" is written, and adjustment has been effected by loading this medium in the floppy disk unit. In other words, the timing adjustment has been effected by the adjustment portion in response to the signal read out from the alignment medium.
In general, the floppy disk unit is constructed such that a motor and a motor driving electric circuit are located under the disk or medium. The above-described adjustment portion is usually provided on the motor driving circuit so that access to this adjustment portion must be made from below the unit. On the other hand, in the manufacturing line, since it is efficient and accurate to carry out a job from above the unit, connecting pins for power supply and signals are connected to connection terminals of each unit from above so as to make each magnetic head move to a required track of the alignment medium to read the signals. In this way, in accordance with the readout signals through the connecting pins connected from above, the adjustment portion is operated from below to thereby effect the index adjustment.
However, if the adjustment portion is located in a position where it is overlapped with the loaded alignment medium as described above, the connecting pins have to be handled from above while the adjustment portion must be adjusted from below. This gives rise to the following problems. Since the adjusting operation is usually performed in a state that the floppy disk unit is put on a pallet, it is necessary to form in each pallet a hole for adjustment to be performed from below. Further, an adjusting tool, for example, a screw driver, must be inserted through a small hole formed in a circuit board so as to be engaged with the adjustment portion, and however, this engagement is not easy and hence the adjusting operation cannot be performed smoothly.
As another prior art, there has been known a floppy disk unit in which an adjustment portion for index signal is so provided as to face upward for the purpose of making it possible to perform the adjustment only by the operation from above. Such a unit is seen in, for example, Japanese Utility Model Examined Publication No. 4-37338. However, this adjustment portion is adapted to detect not the alignment medium but the rotational position of the rotor of a motor.